Audio question

I know this is videolib but I thought some of you folks might be able to
assist me in finding the answer or at least a source for the following query.

Is there a 'standard' for the maximum number of uses/checkouts for an
audiocassette? Or in other words, how many Circs does an audiocassette
have to reach before you should weed it? When has it gone beyond the
tape's actual useful life? Etc.? (Remember, I am talking Audiocassettes
not videos.)

We are trying to set some weeding guideline for our Audiocassette
collection and keep running up against this question. Has any one ever
seen such a number 'printed' anywhere or, perhaps, used in any weeding
policies?

If you know of a source where this question might be put forward more
appropriately please let me know by responding directly to the e-mail
address listed below.